Resilient helix mount for traveling wave tube



p 28, 1965 J. A. LONG ETAL 3,209,198

RESILIENT HELIX MOUNT FOR TRAVELING WAVE TUBE Filed June 28, 1961 O o INVENTORS JAMES A. LONG MARSHALL B. MC DONALD ATTORNEY United States Patent 3,209,198 RESILIENT *I-IELIX MOUNT FOR TRAVELING WAVE TUBE James A. Long, Los Altos, and Marshall B. McDonald,

Palo Alto, Calif., assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed June 28, 1961, Ser. No. 120,228 Claims. (Cl. 3153.5)

This invention relates to traveling wave tubes and in particular to an improved mounting structure for a rod mounted helix in a traveling wave tube.

The difiiculty with mounting a helix and rod assembly Within the envelope of a traveling Wave tube is providing uniform support for the helix over its entire length. Unevenness in the tube wall and in the rods, even though within standard manufacturing tolerances, has an adverse effect on tube performance due to non-concentricity of and uneven rod loading of the helix. Use of rods and tubular members having extremely precise diameters tends to solve this problem but only at considerable increase in cost.

In accordance with this invention, rods and tubes having commercial tolerances can be used in traveling wave tube construction by providing an elongated undulating springlike element between any one of all of the rods and the tube envelope. The spring element is formed to partially fit the contour of the rod so as to seat on the rod and has a longitudinal sinusoidal-like shape so that the element makes springlike contact alternately with the envelope and rod at longitudinally spaced points along the tube. The spring element is fed into the envelope with the helix and rod structure during assembly of the tube and permits removal of the helix and rod structure if disassembly is required. A substantially uniform pressure is exerted by the spring through the rods on the helix. Any unevenness in the diameters of the envelope wall and the dielectric rods is averaged out by the springs so that the helix is supported substantially concentrically on the axis of the tube notwithstanding these irregularities. The spring strips may readily be formed by production techniques from standard strip stock and are therefore very inexpensive to make and handle.

A general object of this invention is the provision of a traveling wave tube with means for supporting the helix about the axis of the tube utilizing commercially available tube envelopes and helix mount rods.

Another object is the provision of a rod mounted helix that is supported throughout its length with substantially constant radial force.

A further object is the provision of an extremely rugged helix-rod mounting structure by which movement of the helix is prevented by a positive longitudinally distributed force applied to the rods against the helix.

Still another object is the provision of resilient means for facilitating insertion and removal of a helix-rod bundle into and from a commercial envelope and for preventing circumferential displacement of the bundle in the tube.

These and other objects of our invention will become apparent from the following description of a preferred embodiment thereof, reference being had to the accompanying drawings in which:

FIGURE 1 is a longitudinal section (partially schematic) of a traveling wave tube embodying our invention;

FIGURE 2 is an enlarged section taken on line 22 of FIGURE 1;

FIGURE 3 is a greatly enlarged portion of FIGURE 1 showing details of the spring construction;

FIGURE 4 is a section taken on line 4-4 of FIG- URE 3;

FIGURE 5 is a section similar to FIGURE 4 showing a form of spring construction; and

FIGURE 6 is a line diagram illustrating the chord-like engagement of the spring with the interior of the envelope.

The traveling wave tube shown in FIGURE 1 comprises a tubular envelope 10 which houses a gun struc ture 11 at one end and a helix 12 within the main body portion of reduced diameter. The helix 12 is supported concentrically of the axis A of the tube by three ceramic rods 13, 14 and 15, see FIGURE 2, circumferentially espaced degrees apart, and which make tangential engagement with successive turns of the helix throughout the length of the helix. The gun portion 11 of the tube produces an electron beam which passes axially down the tube and is collected by the collector 17 at the opposite end. This beam interacts with radio frequency waves on the helix to transfer energy to the waves in the wellknown manner of a traveling wave tube.

The means for coupling the radio frequency Waves to and from the helix have been omitted for sake of clarity of the drawings.

The rods 13, 14 and 15, which may or may not be identical, extend from rod mounts 18 and 19 near opposite ends of the tube and furnish the radial and longitudinal support for the entire helix. In accordance with this invention, one or more of these rods is spaced from and supported on the inner surface 10a of tube 10 by an elongated longitudinally extending spring element 20 which extends a substantial portion of the length of the helix.

Each spring element 20 comprises a single strip of .spring metal and has a longitudinally undulating configuration defining a series of rounded projections 21 spaced apart by depressions 22. Each depression is formed with a transverse concavely shaped seat 23 which engages a limited portion of the periphery of the adjacent rod 13. The projections 21 bear against the inner surface of envelope 10 as shown more clearly in FIGURE 6, and exert a radially inward force against rod 13 which in turn transmits this force to the helix 12. This action of spring 20 is effective throughout substantially the major portion of the length of the helix.

Since the length of each .spring element 20 corresponds generally to the length of the helix being supported, variations in dimensions and straightness of the envelope 10 and of the helix support rod are averaged out over the length of the spring element. The engagement of the spring element with envelope 10 and with the rod, while snug, permits sliding movement of the spring relative to the envelope and rod so that the axial length of the spring can vary slightly with changes in radial pressure along.

the spring, and there is a substantially uniform longitudinal distribution of radial forces exerted by the spring against each of the rods.

The semi-cylindrical concave seat 23 formed in each depression 22 of the spring effectively locks the spring to the rod and insures its proper circumferential position with respect to the rod at all times. The width of seat 23 may be less than the width of the spring as shown in FIGURE 4 or may be equal to the spring width as shown in FIGURE 5.

Spring elements 20 are inserted into the envelope simultaneously with insertion of the rod and helix structure into the tube. Each spring element is fed onto a rod as the latter is moved into the tube. To prevent binding and to facilitate sliding action of the assembly during this operation, any lubricant suitable for use on vacum elements, such as alcohol, may be added. The uniform pressure of the spring element over its entire length against each rod serves to resist angular displacement of the rod within the tube. The uniform distribution of radial force exerted by the springs against the rods centers the helix so that it is essentially concentric with the axis of the tube over the length of the helix.

If disassembly of the tube is required, removal of the rod and helix structure from one end of the tube is facilitated by the presence of the spring elements 20.

The projections 21 of the spring preferably are transversely straight so that the outer spring surface 20a has a chord-like engagement With the envelope inner surface a as shown in FIGURE 6. Thus the spring engages the envelope along the limited area at the spring edges 20c and 20d and tends to bite into the tube so as to resist circumferential displacement of the rod and helix. However, the limited engagement area facilitates longitudinal sliding relative to the envelope and greatly simplifies assembly operations. When the tube is baked out during final stages of assembly, spring edges 20c and 20d become embedded in the heat-softened envelope and are thus locked in position both longitudinally and circumferentially. The entire helix-rod bundle is prevented from shifting and a ruggedized construction is obtained.

Changes, modifications and improvements to the above described preferred embodiment of our invention may be made by those skilled in the art without departing from the spirit and precept of the invention. The scope of the invention is defined in the appended claims.

We claim:

1. A traveling wave tube having an elongated envelope of circular cross-section disposed concentrically about the axis of the tube, a gun at one end of the tube for projecting a beam of electrons down the axis of the tube, a helical transmission line disposed within the envelope concentrically of the axis of the tube, a plurality of longitudinally extending circumferentially spaced rods engaging the exterior of said helix, and an elongated spring element disposed between and engaging one of the rods and adjacent portions of the envelope, said spring element having a longitudinally unduating configuration and exerting a radial spring pressure through said one rod on said helix throughout substantially the length of the helix whereby to support the helix concentrically of the axis of the tube.

2. A traveling wave tube having an elongated envelope of circular cross-section disposed concentrically about the axis of the tube, a gun at one end of the tube for projecting a beam of electrons down the axis of the tube, a helical transmission line diposed within the envelope concentrically of the axis of the tube, a plurality of longitudinally extending circumferentially spaced rods engaging the exterior of said helix, and an elongated spring element disposed between and engaging one of said rods and adjacent portions of the envelope, said spring element having a longitudinally undulating configuration and exerting a radial spring pressure through said one rod on said helix throughout substantially the length of the helix whereby to support the helix concentrically of the axis of the tube, the portions of said spring element which engage said one rod being recessed whereby the element is seated on the rod.

3. In a traveling wave tube having a cylindrical envelope extending along the axis of the tube, a helical line within said envelope, a plurality of non-conducting cylindrical rods extending parallel to the tube axis and engaging the helix throughout its length at circumferentially spaced points, and an elongated spring element disposed between one of said rods and the inner surface of said envelope, said spring element having a sinusoidal-like shape with outwardly extending longitudinally rounded projections engaging the envelope and inwardly extending depressed portions engaging the rod, said projections being transversely fiat and having side edges making contact with the envelope along said edges and being spaced from the envelope intermediate said edges, each of said depressed portions having a longitudinal recess for seating the spring element on the rod.

4. In a traveling wave tube having a cylindrical envelope extending along the axis of the tube, a helical line within said envelope, a plurality of non-conducting cylindrical rods extending parallel to the tube axis and engaging the helix throughout its length at circumferentially spaced points, and an elongated element disposed between one of said rods and the inner surface of said envelope, said spring element having a longitudinal series of outwardly extending projections and inwardly extending depressed portions, said projections making contact with the envelope over less than the transverse dimension of the projection, each of said depressed portions having a seat engaging the rod.

5. In a traveling wave tube having a cylindrical envelope extending along the axis of the tube, a helical line within said envelope, a non-conducting cylindrical rod extending parallel to the tube axis and engaging the helix throughout its length, and an elongated spring element disposed between said rod and the inner surface of said envelope, said spring element having outwardly extending longitudinally rounded projections engaging the envelope and inwardly extending depressed portions engaging the rod, said projections having laterally spaced edges engaging the envelope and being spaced from the envelope intermediate said edges, each of said depressed portions having a longitudinal recess for seating the spring element on the rod.

References Cited by the Examiner UNITED STATES PATENTS Re. 22,461 3/44 Kronheim 2671 Re. 22,495 6/44 Freund 267-1 2,757,310 7/56 Robinson et al. 3153.5 2,806,169 9/57 Robertson et al. 3153.5 2,806,170 9/57 Bianculli 315-35 2,922,068 1/60 Kennedy 3153.6 3,026,445 3/ 62 Staerck 315-3.5

HERMAN KARL SAALBACH, Primary Examiner.

JOHN W. HUCKERT, Examiner. 

1. A TRAVELING WAVE TUBE HAVINAG AN ELONGATED ENVELOPE OF CIRCULAR CROSS-SECTION DISPOSED CONCENTRICALLY ABOUT THE AXIS OF THE TUBE, A GUN AT ONE END OF THE TUBE FOR PROJECTING A BEAM OF ELECTRONS DOWN THE AXIS OF THE TUBE, A HELICAL TRANSMISSION LINE DISPOSED WITHIN THE ENVELOPE CONCENTRICALLY OF THE AXIS OF THE TUBE, APLURALITY OF LINGITUDINALLY EXTENDING CIRCUMFERENTIALLY SPACED RODS ENGAGING THE EXTERIOR OF SAID HELIX, AND AN ELONGATED SPRING ELEMENT DISPOSED BETWEEN AND ENGAGING ONE OF THE RODS AND ADJACENT PORTIONS OF THE ENVELOPE, SAID SPRING ELEMENT HAVING A LONGITUDINALY UNDUATING CONFIGURATIN AND EXERTING A RADIAL SPRING PRESSURE THROUGH SAID ONE ROD ON SAID HELIX THROUGHOUT SUBSTANTIALLY THE LENGTH OF THE HELIX WHEREBY TO SUPPORT THE HELIX CONCENTRICALLY OF THE AXIS OF THE TUBES. 